A Multi-Wavelength Study of Spiral Arm Substructure

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Abstract

Spiral arms are the hallmark of spiral galaxies. Spiral density waves gather gas, dust, and stars in the disks of spiral galaxies, forming the arms. Observations show that these large-scale features are often composed of smaller scale substructures, commonly referred to as feathers and spurs, which give the arm a patchy and segmented
appearance. Within these select galaxies, the substructure appears associated with much of the star formation in the arm. In this thesis, we study the frequency and characteristics of spiral arm substructure in a sample of 233 spiral galaxies; using newly acquired high-resolution (&sim4&rdquo;) CARMA CO(1-0) velocity-integrated intensity maps of five target spiral galaxies, we compare the distribution of star formation tracers along spiral arms and test formation theories for spiral arm substructure.
We use a multi-wavelength data set to study the frequency and characteristics of spiral arm feathers and test the predictions for their formation. Using broadband HST images, we study how common feathers are in our sample of 233 spiral galaxies. With high-resolution CARMA CO(1-0) observations of five target galaxies previously known to have feathers, we study the distribution of the molecular gas relative to the location of neutral gas and star formation tracers. We measure the spacing between the feathers and use the CO(1-0) observations to estimate the molecular gaseous surface density along the spiral arms.
We find that feathering substructure is not limited to late type, grand design spiral galaxies and is detected in a range of galaxy types, from early to late type, and spiral arm environments, including barred, ringed, and flocculent. In our target sample, we find that feathers are more than mere extinction features and are associated with a significant amount of the star-forming gas. We further find a relationship between the spacing of feathers and the gaseous surface density along spiral arms, which suggests these features form via a gravitational instability.